190 Million Year Old Dinosaur Embyro

leprasmurf writes "Sci Tech Today is reporting that scientists have cracked open a 190-million-year-old egg to reveal the oldest known dinosaur embryo. Examination of the fetal skeleton suggests the hatchling would have required parental care to survive. This would be the earliest evidence of nurturant behavior, more than 100 million years earlier than previous examples." The University of Toronto has a release about this as well. From the article: "According to Reisz, what makes this discovery particularly significant is the ability to put the embryos into a growth series and work out for the first time how these animals grew from a tiny, 15 centimetre embryo into a five metre adult. 'This has never been done for a dinosaur. Only Massospondylus is represented by embryos as well as by numerous articulated skeletons of juveniles and adults. The results have major implications for our understanding of how these animals grew and evolved,' he says."

Comments

Here's a picture:

[SilentShriek]

from the NY Times

Pictures

[cyber_rigger]

http://www.news24.com/News24/Technology/News/0,,2- 13-1443_1745931,00.html

Re: Embryonic Bones & Actual Dinosaur Blood

[Black Parrot]

> In a report titled "Scientists Discover T. Rex. Soft Tissue" distributed by NBC on its website, scientists have actually obtained the blood samples of the most famous dinosaur: Tyrannosaurus Rex.

No, just "blood vessels", and even that is controversial. The apparently solid result is the discovery of medullary bone in the leg. Notice the abstract of the paper at the bottom of the link: no mention of blood, or even vessels.

I think the claims about finding vessels is just a misunderstanding of the fact that bones have holes where the blood vessels run, and the medullary bone was found in those holes.

I took classes with Dr. Reisz...

[Fulg0re-]

I had the opportunity to actually take several courses with Dr. Reisz several years ago at UTM, including my first introduction to human anatomy and physiology course. At the time, I was certainly surprised to learn about the homology that musculoskeletal systems had across species, even those separated by millions of years of evolution.

I was also farily surprised to learn about some of the more optimal "solutions" that evolution came up with, including things such as the development of the cardiovascular systems ranging from say two-chambered hearts, to four-chambered hearts.

It's also very sensible to presume that quadrapeds eventually evolved into bipeds in some dinosaur species. Of course, all we needed was proof for that assumption, and that's what this discovery was all about.

Is it possible that the species found in the egg had congenital defects or was simply too small for its developmental age? Highly unlikely in my opinion. Too many other morphological factors involved.

Precocial or altricial?

[TFGeditor]

From the article: 'The third area, he said, is the most speculative. Some of the embryos were clearly ready to hatch, he said, but they have no teeth, "and that suggests to us that some form of parental care was required ... not just protecting but active feeding." '

Speculating on whether hatchlngs were precocial or altricial based on absence of teeth is quite a stretch.

Among birds, most birds that spend most of their time on the ground walking are born precocial (feathered, able to walk and feed minutes after hatching). Birds that spend most of their time in trees and flying are altricial (naked, unable to fly, walk, or feed themselves and hence need parental nurturing fore some time).

However, coupled with other clues from the article, the altricial speculation seems more credible: "...the proportions of the limbs, neck and head suggest that as a baby and young animal this species walked on four legs, but as an adult it was able to walk on two legs some of the time." And, "...Mr. Reisz and colleagues reported that the Massospondylus hatchling was born four-legged with a relatively short tail, a horizontally held neck, long forelimbs and a huge head. As the animal matured, the neck grew faster than the rest of the body, but the forelimbs and head grew more slowly. The end result was a two-legged animal that looked very different from the four-legged embryo. Mr. Reisz suggested that the change from four- to two-legged could be a matter of balance related to the development of the animal's neck."

The long neck suggests adult animals were browsers rather than grazers. As such, young clearly could not feed except on very low-growing shrubs. On the other hand, perhaps the young grazed during development and gradually adapted to browsing. If so, it further erodes the altricial speculation.

Altricial young usually lack an ability critical to survival (e.g. flight among birds, foraging/hunting among mamallian carnivores and omnivores such as bears and chimpanzees) that involves both post-natal development and learning by minicry of the parents.

Precocial young (common in most mammalian herbivores) have essential abilities (feeding, mobility--to feed, keep up with herd, escape predators) from birth often as an adaptation to allow "following the food." It therefore seems unlikely that an herbivorous species would bear altricial young because it would tie parents to a location during post-natal development, and the copious quantities of vegetation required by such large animals would deplete immediate-area resources rather quickly.

Lack of teeth does not preclude suckling, another trait common among precocial herbivores.

My vote therefore goes for precocial.